Add a selftest that creates a tap device, attaches XDP and TC programs,
writes a packet with a test payload into the tap device and checks the
test result. This test ensures that the XDP metadata support in the tun
driver is enabled and that the metadata size is correctly passed to the
skb.

See the previous commit ("selftests/bpf: refactor xdp_context_functional
test and bpf program") for details about the test design.

The test runs in its own network namespace using the feature introduced
with commit c047e0e0e435 ("selftests/bpf: Optionally open a dedicated
namespace to run test in it"). This provides some extra safety against
conflicting interface names.

Signed-off-by: Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>
---
 .../bpf/prog_tests/xdp_context_test_run.c     | 59 +++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
index 78ca01edb050..ce3e82cc69d1 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
@@ -8,6 +8,7 @@
 #define TX_NAME "veth1"
 #define TX_NETNS "xdp_context_tx"
 #define RX_NETNS "xdp_context_rx"
+#define TAP_NAME "tap0"
 
 #define TEST_PAYLOAD_LEN 32
 static const __u8 test_payload[TEST_PAYLOAD_LEN] = {
@@ -255,3 +256,61 @@ void test_xdp_context_veth(void)
 	netns_free(tx_ns);
 }
 
+void test_ns_xdp_context_tuntap(void)
+{
+	LIBBPF_OPTS(bpf_tc_hook, tc_hook, .attach_point = BPF_TC_INGRESS);
+	LIBBPF_OPTS(bpf_tc_opts, tc_opts, .handle = 1, .priority = 1);
+	struct test_xdp_meta *skel = NULL;
+	__u8 packet[sizeof(struct ethhdr) + TEST_PAYLOAD_LEN];
+	int tap_fd = -1;
+	int tap_ifindex;
+	int ret;
+
+	tap_fd = open_tuntap(TAP_NAME, true);
+	if (!ASSERT_GE(tap_fd, 0, "open_tuntap"))
+		goto close;
+
+	SYS(close, "ip link set dev " TAP_NAME " up");
+
+	skel = test_xdp_meta__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open and load skeleton"))
+		goto close;
+
+	tap_ifindex = if_nametoindex(TAP_NAME);
+	if (!ASSERT_GE(tap_ifindex, 0, "if_nametoindex"))
+		goto close;
+
+	tc_hook.ifindex = tap_ifindex;
+	ret = bpf_tc_hook_create(&tc_hook);
+	if (!ASSERT_OK(ret, "bpf_tc_hook_create"))
+		goto close;
+
+	tc_opts.prog_fd = bpf_program__fd(skel->progs.ing_cls);
+	ret = bpf_tc_attach(&tc_hook, &tc_opts);
+	if (!ASSERT_OK(ret, "bpf_tc_attach"))
+		goto close;
+
+	ret = bpf_xdp_attach(tap_ifindex, bpf_program__fd(skel->progs.ing_xdp),
+			     0, NULL);
+	if (!ASSERT_GE(ret, 0, "bpf_xdp_attach"))
+		goto close;
+
+	/* The ethernet header is not relevant for this test and doesn't need to
+	 * be meaningful.
+	 */
+	struct ethhdr eth = { 0 };
+
+	memcpy(packet, &eth, sizeof(eth));
+	memcpy(packet + sizeof(eth), test_payload, TEST_PAYLOAD_LEN);
+
+	ret = write(tap_fd, packet, sizeof(packet));
+	if (!ASSERT_EQ(ret, sizeof(packet), "write packet"))
+		goto close;
+
+	assert_test_result(skel);
+
+close:
+	if (tap_fd >= 0)
+		close(tap_fd);
+	test_xdp_meta__destroy(skel);
+}
-- 
2.43.0

On 02/27, Marcus Wichelmann wrote:
> Add a selftest that creates a tap device, attaches XDP and TC programs,
> writes a packet with a test payload into the tap device and checks the
> test result. This test ensures that the XDP metadata support in the tun
> driver is enabled and that the metadata size is correctly passed to the
> skb.
> 
> See the previous commit ("selftests/bpf: refactor xdp_context_functional
> test and bpf program") for details about the test design.
> 
> The test runs in its own network namespace using the feature introduced
> with commit c047e0e0e435 ("selftests/bpf: Optionally open a dedicated
> namespace to run test in it"). This provides some extra safety against
> conflicting interface names.
> 
> Signed-off-by: Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>

Acked-by: Stanislav Fomichev <sdf@fomichev.me>